Steering devices are provided at the rear side of marine vehicles such as vessels to change the direction of movement both in forward and backward directions while maneuvering, such devices consist mainly of an arm, a shaft, and a rudder.
In a typical shaft-rudder construction, vertical axis of the rudder shaft becomes positioned on the front of the rudder when the marine vehicle moves forward, and since the area on the rudder's front section that is exposed to water load during forward motion is relatively small, the rudder can be easily controlled. In other words, since no rudder area is left on the front of the rudder shaft while moving forward, water cannot exert force on such ‘non-present’ area, which provides an easy control of steering attempts of the vessel.
The preceding condition, however, is much different as such vessel moves backward. In other words, the vertical axis of the rudder shaft becomes positioned on the rear with respect to the rudder's surface area, exposing the rudder's area to water load when the vessel moves backward, and making difficult to control the rudder and exposing the mechanical components thereof to external forces.
The disadvantages are proposed to be addressed in U.S. Pat. No. 7,806,068 issued to the same inventor. In essence, the rudder device of U.S. Pat. No. 7,806,068 comprises an arrangement attached to the vertical rudder shaft in a way to rotate the rudder around an axis perpendicular to the lateral surfaces thereof at an upper side of the rudder. Rotation of the rudder is achieved by a drive, such as piston extending substantially in vertical direction and connected to the vertical rudder shaft from one end and to the rudder from the other end.
While the rudder mechanism of U.S. Pat. No. 7,806,068 provides an effective solution for the purpose, it may not always exhibit a robust rudder structure under the impact of high water forces due to relatively insubstantial constructional structure with the vertical rudder shaft. This may be particularly important as far as relatively large sized sailboat rudders are concerned. On the other hand, positioning of the drive element of U.S. Pat. No. 7,806,068 in vertical direction requires higher moment forces to rotate the rudder rotation axis since the directing of the moment force comes close to the rudder rotation axis.